Faulty power supply

36 posts in this topic

I have just built a regulated PSU (+/- 15v) for a pre amp. Quasar kit 1216 for the CCT diagram,http://www.quasarelectronics.com/1216.htm. When testing the voltages wrt ground, I initially got +/- 15. But the voltages started to creep up slowly until one of the caps went pop at about 24v . I checked and replaced the 15v zenner's and the damaged cap and checked again. Still the same, but this time I turned it off before the voltage got too high.

I have thoroughly checked the board against the CCT diagram and also checked for cold/dry joints. All the diodes and electrolytic caps are the correct way round and no short CCT's. The CCT uses LM317/337T voltage regulators.

Correct me if I am wrong, but the zener diodes are there to limit the voltage to the variable voltage regs ?If that is the case then there must be something wrong a) with the diodes (you say you replaced these and the problem persists) or b) the circuit. The LM 317 is designed to go up to 37v.

This may be a stupid comment, but why not make the PS with 7815/7915's ?

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I have just built a regulated PSU (+/- 15v) for a pre amp. Quasar kit 1216 for the CCT diagram,http://www.quasarelectronics.com/1216.htm. When testing the voltages wrt ground, I initially got +/- 15. But the voltages started to creep up slowly until one of the caps went pop at about 24v . I checked and replaced the 15v zenner's and the damaged cap and checked again. Still the same, but this time I turned it off before the voltage got too high.

I have thoroughly checked the board against the CCT diagram and also checked for cold/dry joints. All the diodes and electrolytic caps are the correct way round and no short CCT's. The CCT uses LM317/337T voltage regulators.

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It looks like D12 is dead anyway. 27ohm's (R18)either way through the diode wrt -ve. I'll change it when I get home. I hope it works. I also have Quasar on the case. They are going to speak to the kit manufacturer to see if they have any ideas.Quasar have been most helpful.